Deep in the jungle, armed forest rangers trek through the palms on a mission to confirm some rare good news: the discovery of a wild tiger population in an area of Thap Lan national park previously written off by wildlife experts.

Working with foreign conservationists, the rangers have been gathering evidence from camera traps over the past two years that suggests this single national park in Thailand may have more tigers than China.

Thap Lan, with its spectacular forests of saw-bladed plan palms, is an oasis of biodiversity amid expanding human development. Elephants, clouded leopards, spotted linsang, boar and deer thrive below the canopy, which is filled with the song of myna, lapwings, laughing thrushes and other exotic birds.

Locals have long insisted that tigers also prowl in this area. Camera traps, triggered by heat and movement, have been left strapped to trees for a month. Some have been destroyed by wild elephants or infested by nesting ants, but the memory cards inside have yielded a treasure trove of images of bears, leopards, itinerant monks, as well as tigers and – worryingly – armed poachers.

More than half the park has still to be checked, but rangers have already confirmed eight tigers. This is not yet enough to be classified as a sustainable population, but park managers are optimistic more animals will be found. "I'm very happy as this is beyond expectations," said Thap Lan's superintendent, Taywin Meesap. "There are areas deeper inside where we haven't placed camera traps yet. Given the results so far, there could be 20 to 50 tigers here."

The conservation group that provided much of the training and equipment for the operation said the results showed a gap in understanding and the need to invest more in research and protection.

Tim Redford of Freeland, a Bangkok-based group that helps rangers in south-east Asia, said: "This place was supposed to be devoid of tigers. But we did a course here and were surprised to find signs of tigers. The more we looked, the more we found. That led me to believe the forest must have tigers throughout and there is a big gap in our knowledge of where they live."

He called for further studies across countries where other small populations may have been missed.

The difficulty of measuring tiger numbers was evident when India increased its estimate by 10% compared with a survey in 2008.

The discovery comes amid a fresh global push to reverse a precipitous decline in the numbers of wild tigers, down 97% compared with a century ago. At the St Petersburg tiger summit last year, participants, including the World Bank, NGOs and range states, pledged $329m (£200m) to help double the predators' numbers in the wild from the current level of about 3,200.

But the new hope in Thap Lan is mixed with old fears. Thailand is thought to be home to between 250 and 300 wild tigers, but they are vulnerable. The biggest threat is a loss of habitat. Although nominally protected, Thailand's national parks are being encroached upon by human development, particularly monoculture plantations, roads and second homes for Bangkok's rich.

Many locals also subsidise their incomes by poaching and illegally logging aloe and tropical hardwood. Park managers and police are worried that poachers and illegal traders would target the tigers once news gets out about their numbers in the area.

Rangers mount night patrols and public education campaigns to halt these activities. It can be dangerous work. A Thap Lan ranger was killed in a gun battle with poachers three years ago. In Cambodia, forest protectors have been murdered in hand grenade attacks.

The stakes are high. According to conservationists and police, poachers are paid 7,000 to 15,000 baht – £150 to £300 – per kg for a tiger carcass.

Middlemen then sell the animals on for about 10 times that amount, mostly to customers in China and Vietnam, where the animal's bones and penis are used in tonics and aphrodisiacs. Yet penalties for wildlife offences remain absurdly low, with fines ranging from 500 to 40,000 baht.

Thailand has much to protect. The country is home to some of the most biodiverse tropical forests in south-east Asia. Just two hours from Bangkok, the Guardian's car almost ran over a King Cobra, which expressed its indignation by rearing up angrily and flickering its tongue.

Despite this ecological wealth, wildlife crime was a low priority for law enforcement authorities for many years. But there are signs that attitudes may be changing. Thai customs officials have made several high-profile arrests in the past two years, including that of a woman who attempted to smuggle a live baby tiger cub through Bangkok airport in a case full of stuffed animal toys.

More impressive still was an undercover operation by the Thai police this year that exposed a large tiger-trading syndicate. Its ringleader, a woman known as "J", remains at large, partly because her husband is a police officer, but investigators said they were closing in.

"I believe she may have been selling 100 tigers per year for 10 years," said Colonel Kittipong Khawsamang, deputy head of the wildlife crime division as he leafed through police photographs of tiger carcasses kept on ice.

"We know she is a big trader and have been collecting evidence, but we don't yet have enough for a prosecution."

Khawsamang said recent raids have shown Thailand has become a hub of the tiger trade, due to its location between other range nations in south-east Asia and China, the main market.

The business is also supplied by Thailand's many tiger farms, some of which claim to operate as zoos while covertly breeding animals for sale. The most notorious is the Sri Racha zoo near Pattaya, which police have raided on several occasions, confiscating hundreds of animals.

Tourists still flock to watch the farm-bred tigers jump through flaming hoops, suckle at pigs and walk around on their hind legs to the music of the Can-Can and laughter from the audience.

Police and conservationists believe "zoos" encourage poaching both as a source of breeding stock and by sustaining the market for tiger products.

General Misakawan Buara, commander of Thailand's natural resources and environmental crime division, said: "The problem is, we can only check permits and the inventory, but we can't check which tigers and going in and out because we are police, not animal experts. We need more DNA checks, implanted chips or a tagging system so we can verify the origins of tigers."That – like training and equipping rangers – is not cheap. But little of the money pledged at St Petersberg summit is evident yet at the grass roots, where the budgets for rangers and wildlife police are unchanged "Tiger conservation at the top and the bottom are two different worlds.

The people who are high paid researchers and biologists jet-set around the world," said Freeland's Redford.

"The rangers are paid almost nothing. They get $50 to $200 a month to go out and face armed poachers. We need to give them every support we can if we expect to keep tigers into the future.

"There is not a shortage of money, we just have to get it focused in the right places."

Tiger number

There are believed to be about 3,200 tigers left in the wild and more than 13,000 in captivity – half of which are in China.

Assessing populations in the wild is notoriously difficult, given the remoteness of the habitat and the animals' tendency to avoid human contact. It is believed numbers have fallen by 97% over the past century and the trend remains downwards, but several revisions have taken place in recent years.

• In March, India unveiled a new census that put the total number of wild tigers in the country close to 1,550 – 10% up on 2008.

• In Indonesia, camera traps have recently caught images of 12 Sumatran tigers, including a mother playing with cubs. The WWF estimates there are only 400 Sumatran tigers left in the wild. A recent study conducted by Wildlife Conservation Sociey said the population could be much larger than previously believed.

• About 350 adult Siberian or Amur tigers – physically, the largest subspecies – are left in the wild, with 95% inhabiting the far east of Russia.

• Thailand is thought to be home to 250 to 300 wild tigers, though camera traps have revealed that Thaplan National Park has more of the animals than previously believed.

• Bangladesh has between 400-450 wild tigers, mostly in the Sunderbans mangrove forests which overlap with India. Last year, they killed 44 people.

Jonathan Watts

• This article was amended on 17 May 2011. The original referred to Thap Lan's superintendent as Taywin Meesat. This misspelling has been corrected.

Burma border markets act as deadly trade gateway for tigers, shows a report published by Traffic and WWF, as an International Tiger Forum is held in St Petersburg in a bid to protect the big cats, which have declined a staggering 97% over a century